Protective system



Dea-2s, 1948. G. D. HANCHETT, JR' 2,457,663

PROTECTIVE SY STEM Filed March 16, 1946 PZA INV EN TOR.

mae/wry Patented Dec. 28, 1948 PROTECTIVE SYSTEM George D. Hanchett,l Jr., Millburn, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application March 16,1946, Serial No. 654,862

'z claims.` (C1. 315-276) This invention relates to protective systems such as are useful in producing an effect in response either to a relatively low impedance or to a relatively high impedance between a pair of 'conductors which may be, for example, the two rails of a railway crossover or the like.

-It is well known that there exists between the rails' of any section of a railway an impedance which varies with the weather from a relatively low vimpedance in wet weather to a relatively high impedance in dry weather. Such variation in impedance is denoted herein as the normal range of Variation in the impedance between the two rails or conductors. Any protective system associated with such conductors (1) should be insensitive to this normal range of variation in the impedance, and (2) should be sensitive to impedances outside this normal range. Thus, in the case` of a short circuit between the two conductors'when the impedance is below the normal range, the protective system should produce an' effect such as the lighting of a red signal. Iiikewise, in the case of an open or faulty circuit, when the impedance is above the normal range', the protective system should produce the same effect.

e In a copending application of Hubert H. Wittenberg, Serial No. 631,723, led November 29, 1945, is disclosed such a protective system wherein y(1) v a unilateral impedance device such as a rectifier is connected between the conductors at one'hof their ends, (2) an alternating potential input means and a resistor are conected in series between the conductors at the other of their ends,4(3) a pair of electron discharge devices in push-pull relationship each has applied tol its anode and shield grid alternating potentials which are arranged to be of ropposite polarity for ensuring its deenergization when the potential of its control grid decreases to'a predetermined critical value, (4) alternating potential bias means are connected between the conductors or rails and the control grid circuits of the two electron discharge devices so that one ofthe devices is deenergized during the positive half cycle of its anodeI .potential in response to an impedance lower than the normal range and the other of said devices is deenergized during the negative half cycle of its anode potential in response to an impedance higher than the normal range, and (f5) vthecathode heaters of the two devices are each connected in series with its shield or screen grid so that the electron emission of the device is interrupted in response to openingof the screen grid circuit.

The vprotective system of the present invention is'an improvement on that of the aforesaid copending application and affords added protection against failure of the protective system due to (1) all open or short circuits in the electron discharge devices themselves, and (2) short or open circuits in the various circuit components such as theresistor, capacitors, the rectiiier, the transformer windings, etc. While the achievement of these additional results involve certain modications'of the system disclosed by the aforesaid copending application, the two systems are basically the same and involve the same mode of operation..

Important objects of the present invention are the provision of an improved protective system of the type which operates to produce a danger signal in response to an abnormal impedance between two conductors, and the provision of a protective system which functions to produce such adanger signal in response to failure of any of its components.

The invention 4will be better understood from the following description considered in connection with the accompanying drawings and its scope is indicated by the appended claims.

Referring to the drawing, Fig. 1 is a wiring diagram of the improved protective system, and Fig. 2 is an explanatory diagram relating to the operation of the system as affected by short or open circuits of certain resistors R3 and R4.

This system includes a pair of conductors I0 and II, Connected between these conductors at one of their ends is a unilateral impedance device such as a rectier i2. At the other of their ends, the two conductors are interconnected through a resistor I3 and alternating current in` put means shown as the secondary winding I4 of a transformer.

A pair of .electron discharge devices I5 and I6 lconnected in push-pull relationship have their various operating potentials applied from the transformer secondary windings I'l, I8, I9 and 20 and have their control potentials applied from the secondary winding I4 which is connected between the conductors Ill and II as previously indicated. The various pins or terminals of the device I 5 are-indicated by the reference numerals I to 1 and the corresponding terminals of the device I6 are indicated by the reference numerals I to 'l'. The devices I5 and I6 are preferably of the gaseous conduction type sometimes designat-ed bythe term Thyratron With respect to the device I5, it will be noted (rl) that yits cathode heater isconnected across,

the lower 6.3 volt half of the secondary I4, (2) that its output circuit includes the operating coil of a relay RL--|, the 150 volt secondary Il, the shield grid 2|, an adjustable part of a resistor R4 and the lower mid-section of the secondary I9, (3) that its shield grid potential is determined by the lower mid-section of the secondary I9 and the secondary I8, and (4) that its control grid potential is applied through a resistor R5 from an 8 volt tap of the secondary I4. The operating coil of the relay RL-I is shunted by a capacitor C1 and a resistor R1.

Similarly with respect to the device I 6 it is seen (l) that its cathode heater is connected across the upper 6.3 volt half of the secondary I9, (2) that its output circuit includes the operating coil of a relay RL-2, the 150 volt sec ondary 20, the shield grid 22, an adjustable part of a resistor Rg and the upper mid-section of the secondary I9, (3) that the potential of its shield grid 22 is determined by the upper mid-section of the secondary I9 and the secondary I8, and (4) that its control grid potential is applied through a resistor Re from the conductor II. Connected in shunt to the operating coil of the relay RL-Z are a capacitor C2 and a resistor Rz.

The relays RL--I' and RL-2 are series connected in a control circuit in a well known manner so that deenerization of either oi them actuates a controlled device such as a danger signal. l

So long as the impedance between the conductors III and II is within its normal range and there are no defects in the protective system, the devices I5 and I6 are energized due to the fact that their control grid potentials are more positive than the critical voltage at which they are deenergized. When the impedance between the conductors I and II is below its normal value and that the polarity is such that the conductor I I is positive, 1) the voltage between the conductors Ill and II is reduced due to the increase in current through the resistor I3, and (2) the grid potential of the device I6 is reduced below its critical value so the device I6 is deenergized. When the polarity is such that the conductor I0 is positive and the combined series impedance of conductors I0 and II and the rectifier I2 is above its normal value (l) less current is drawn through the resistor I3, and (2) the grid potential of the device I is reduced below its critical value so that the device I5 is deenergized.

Deenergization of the electron discharge de vices and relays is also produced by various kinds of defects in the protective system.

Considering first open circuits between the different terminals of the device I5, it is seen that the device I5 and the relay RL-I are deenergized in response to an open circuit at (1) the terminal I which will remove the signal from the device I5 which is operated as a positive grid tube by the use of a negative voltage on the shield' grid 2I, (2) the terminal 2 which will interrupt the plate circuit of the device I5, (3) the terminal 3 or 4 which will interrupt the heater circuit, (4) the terminal 5 or 1 which will interrupt the plate circuit, or (5) the terminal 6 which will interrupt the plate circuit. The effects of open circuits on the device I6 are similar to those stated in connection with Fig. 2.

The device I5 and the relay RL-l are deenergized in response to a short circuit between (1) the terminals I and 2, 3 or 4 which removes the control signal from the device I5 and places areduced voltage on the grid while the anode is positive, (2), the terminals I and 5 or I which places a negative voltage on the control grid while the anode is positive, (3) the terminals I and 6 which places suiicient alternating potential across the coil of relay RL--I to open its circuit (R5 must be low enough in value that enough alternating current is drawn through the relay coil RLk-I to deenergize it. The saine is true o! Re), (4) the terminals 3 and 2 or 4 which interrupts the electron emission, (5) the terminals 6 and 2, 3 or 4 which places sufficient alternating potential across the coil oi relay RL-I to open it, (6) the terminals 5 and 5 or l which places sufficient alternating potential across the coil of relay RL-I to open it, and ("1) the terminals l or 1 and 2, 3 or 4 which reduces the shield voltage of the device I5 to zero.

In connection with the last item (7), it should be understood that a short circuit between the terminals 5 or I and 2, 3 or 4 short circuits the lower mid-section of the secondary I9 thus reducing the load on the secondary I8 so that the secondary I8 draws less current through the upper mid-section of the secondary I9 and the right hand section of the resistor R3 thereby applying to the shield grid 22 of the device I6 a more nega.- tive voltage by which the device I6 and the relay RL-Z are deenergized. In like manner, the device I 5 and the relay RL--I' are deenergized in response to a short circuit between the terminals 5' or I and 2', 3 or 4 of the device I6. What has been said of other defects oi the device Il is also true of the device I6.

With respect to short circuits or open circuits in the various components of the system, it is seen that either a short or open circuit in C1 or R1 will reduce the unidirectional voltage across the relay RLI to a value at which the relay RL-I opens and that the relay RL-2 similarly opens in rel spouse to open or short circuits in C2 or Rz.

With respect to the resistor R3, a short circuit between its terminals A and B makes the shield grid 22 more negative thus deenergizing the device I5 and relay RL-I, an open circuit at the terminal A makes the shield grid 22 more negative thus deenergizing the device I5 and the relay RL-I, an open circuit at the terminal B makes the shield grid 22 more negative thus deenergizing the device I5 and relay RL-I and an open circuit in the movable :contact lead opens the anode circuit of the device I5 and deenergizes the relay RL-I. The effects of defects in the resistor Rl are similar to those set forth in connection with the resistor R3.

How these results are produced is evident from the following analysis of Fig. 2: Normal condition,

(a) I5 and l5 conduct on alternate half cycles with I5 conducting.

(b) Plate current in right half of R4 balances voltages of I8 and I9.

(c) A short "I to 2 upsets this balance so that current from IB produces in right half of R: a more negative voltage which is applied to 1 deenergizes I6.

(d) Open at A applies 151.2 v. between 2 and the anode of I5, plate current of I5 (smaller than normal) goes through R3 and left half of R4, 22 is more positive, 2I is much more positive, next half cycle makes 22 more negative and deenergizes I6.

(e) Open at B applies 145.3 v. between 2 and anode of I5, grids 2| and 22 are more positive, next half cycle makes 22 more negative, and deenergizes I6.

An open circuit in the resistor Rs or Re will interrupt the control signal and deenergize the device I5 or I6 to which it is connected. A short circuit on either of these resistors will shorten the life of the device I5 or I6 to which it is connected but will not aiiect the operation of the protective system.

With respect to the resistor I3, (1) an open circuit will remove the voltage between the conductors I and II thus interrupting the control voltage of the device I6 and deenergizing the relay RL-2 and (2) a short circuit will decrease the signal on the device I5 and deenergize the relay RL--L If the rectifier I 2 fails, the device I6 and the relay RL-Z are deenergized. If it is short circuited, the device I5 and the relay RL-I, are deenergized.

Short circuits across any of the windings of the power transformer will burn them out thus removing the voltage across the relay coils. A break in the winding I1 will open the relay circuits. A break in the winding I9 will interrupt the heater current of the device I5 or I6. A break in the winding III will remove voltage from the conductors I0-II while a break in the 8-volt section of this winding will remove signal from the device I5. A break in the winding I8 will increase the negative shield voltage on both devices I5 and I6 thus deenergizing both devices and the corresponding relays.

'I'hus the outstanding characteristic of the improved protective system of the present invention is a circuit arrangement such that the failure of any part likely to affect the operation of the system immediately produces an indication of such failure.

I claim as my invention:

1. The combination of a series circuit including a pair of impedance devices each provided with a terminal intermediate its ends, bias voltage means connected between said impedance means at one of their ends and provided with a midpoint terminal, means connected between said impedance means at the other of their ends for applying a voltage which is opposed to said bias voltage and a value smaller than said bias voltage, and a pair of electron discharge devices having their cathodes connected to the midpoint terminal of said bias voltage means and their shield grids each connected to a different intermediate terminal of said impedance means.

2. The combination of a series circuit including a pair of impedance devices each provided with a terminal intermediate its ends, bias voltage means connected between said impedance means at one of their ends and provided with a midpoint terminal, means connected between said impedance means at the other of their ends for applying a voltage which is opposed to said bias voltage and a value smaller than said bias voltage, a pair of electron discharge devices having their cathodes connected to the midpoint terminal of said bias voltage means and their shield grids each connected to a diierent intermediate terminal of said impedance means, and means for simultaneously applying between the shield grids and anodes of said electron discharge devices plate voltages of opposite polarity.

3. The combination of a series circuit including a pair of resistors each provided with a terminal intermediate its ends. a bias voltage transformer winding connected between said resistors at one of their ends and provided with a midpoint terminal, a transformer winding connected between said resistors at the other of their ends for applying a voltage which has a polarity opposed to that of said bias voltage winding and has a smaller value than said bias voltage, and a pair of electron discharge devices having their cathodes connected to midpoint terminal and their shield grids each connected to a different one of said intermediate terminals.

4. The combination of a series circuit including a pair of resistors each provided with a terminal intermediate its ends, a bias voltage transformer winding -connected between said resistors at one of their ends and provided with a midpoint terminal, a transformer winding connected between said resistors at the other of their ends for applying a voltage which has a polarity opposed to that of said bias voltage winding and has a smaller value than said bias voltage, a pair of electron discharge devices having their cathodes connected to midpoint terminal and their shield grids each connected to a different one of said intermediate terminals, and a pair of oppositely polarized transformer windings each connected between the shield grid and anode of a different one of said electron discharge devices.

5. The combination of a series circuit including a pair of resistors each provided with a terminal intermediate its ends, a bias voltage transformer winding connected between said resistors at one of their ends and provided with a midpoint terminal, a transformer winding connected between said resistors at the other of their ends for applying a voltage which has a polarity opposed to that of said bias voltage winding and has a smaller value than said bias Voltage, a `pair of electron discharge devices having their cathodes connected to midpoint terminal and their shield grids each connected to a different one of said intermediate terminals, a pair of oppositely polarized transformer windings each connected between the shield grid and anode of a different one of said electron discharge devices, a pair of conductors between which there exists a normal range of im pedance variation, and means for applying to the control grids of said electron discharge devi-ces voltages whereby they are selectively deenergized in response to interconductor impedance values which are higher than said range and lower than said range.

6. The combination of an electron discharge device having an anode and a cathode and control and shield grids, a source of potential, and means connecting said anode to'said cathode through said source and said shield grid.

7. The combination of an electron discharge device having an anode and a cathode and control and shield grids, a source of potential, a load device to be operated, and means connecting said anode to said cathode through said source, said shield grid and said load device.

GEORGE D. HANCHETT, J R.

REFERENCES CITED UNITED STATES PATENTS Name Date Schlesinger Nov. 30, 1947 Number 

